Broad classes of semiconductor devices may include several configurations of the same basic device differing in one or more aspects such as output voltage, frequency, trigger temperature, and the like. There are several conventional techniques for providing a specific configuration from a family of devices. In one technique, different versions of the same basic semiconductor are manufactured with slightly different internal component values or configuration to provide the differing outputs. For example, voltage regulators may include a family of devices having various output voltages and tolerance levels. Different devices are manufactured and inventoried by suppliers etc. to provide each of the possible combinations of output voltage and tolerance. An advantage of this approach is that devices with tight tolerances may be provided without the need for expensive external components. However, the cost of the regulators may be higher due to the lower quantities that are produced for each specific voltage/tolerance combination as well as the increased inventory costs.
Another technique uses one or more external components to complete an internal circuit such as an error amplifier for a voltage regulator. Here, the tolerance of the external components has a direct affect on the tolerance of the output that is generated. To attain an output with a tight tolerance, higher priced tight tolerance external components may be required. In addition, a large selection of the tight tolerance external components may be have to be stocked to provide flexibility in setting the output to the desired value.
Shown in FIG. 1A is a third technique for configuring a semiconductor 5. The third technique uses digital input signals to set the semiconductor configuration. Pull-up resistors 6 in combination with switches 7 generate the digital input signals. One digital input may select between two (21) configurations. Two digital inputs may select between four (22) configurations. Three digital inputs may select between eight (23) configurations and so on. To select between a moderate number of configurations, a large quantity of pins may be required. Dedicating four pins merely for selecting between 16 configurations is costly in terms of both, price and package size. Whereas, using two pins for selection may provide reasonable cost and package size, but only provides selection from amongst four configurations.